clc,clear,close;
x=[0 0.5 -0.5 0.625 -0.625 0.75 -0.75 0.875 -0.875 1 -1 1.25 -1.25 1.5 -1.5 1.75 -1.75 2 -2 2.5 -2.5 3 -3 3.5 -3.5];
y=0;
plot(x,y,'+');